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HK: Fachverband Hadronen und Kerne

HK 53: Accelerators and Instrumentation II

HK 53.3: Talk

Wednesday, March 18, 2009, 14:30–14:45, H-ZO 90

An FPGA based preprocessor for the ALICE HLT — •Torsten Alt and Volker Lindenstruth — Kirchhoff Institute of Physics, University of Heidelberg, Germany

With more than 550.000 channels the Time Projection Chamber is the main tracking detector in ALICE. Particles traversing the TPC will create a track of primary ionized electrons which drift towards the read-out pads in the endcaps where they create a charge cloud which is then digitized. To achiev a better spatial resolution than the pad size this charge cluster is spread over several pads. In order to reconstruct the particle trajectories the center of gravity of the clusters needs to be calculated before this information is passed to the tracking algorithms. In the ALICE High-Level-Trigger (HLT) this clusterfinding is done by an FPGA preprocessor. Raw data is received directly from the detector via optical links, unpacked and feed into the Fast-Cluster-Finder (FCF) processing unit which calculates the centers of gravity. The results are then transfered into the main memory of the HLT. The FCF algorithm has been optimized to take advantage of the FPGA resources allowing parallel processing of the data and pipelining resulting in a design speed of more than 150 MHz. First results with simulated data show that the 216 FCF processors in the HLT are able to process an event with about 7200 charged particles in less than 1 millisecond.